[mirror_ubuntu-bionic-kernel.git] / lib / flex_array.c

/*
 * Flexible array managed in PAGE_SIZE parts
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright IBM Corporation, 2009
 *
 * Author: Dave Hansen <dave@linux.vnet.ibm.com>
 */

#include <linux/flex_array.h>
#include <linux/slab.h>
#include <linux/stddef.h>
#include <linux/export.h>
#include <linux/reciprocal_div.h>

struct flex_array_part {
	char elements[FLEX_ARRAY_PART_SIZE];
};

/*
 * If a user requests an allocation which is small
 * enough, we may simply use the space in the
 * flex_array->parts[] array to store the user
 * data.
 */
static inline int elements_fit_in_base(struct flex_array *fa)
{
	int data_size = fa->element_size * fa->total_nr_elements;
	if (data_size <= FLEX_ARRAY_BASE_BYTES_LEFT)
		return 1;
	return 0;
}

/**
 * flex_array_alloc - allocate a new flexible array
 * @element_size:	the size of individual elements in the array
 * @total:		total number of elements that this should hold
 * @flags:		page allocation flags to use for base array
 *
 * Note: all locking must be provided by the caller.
 *
 * @total is used to size internal structures.  If the user ever
 * accesses any array indexes >=@total, it will produce errors.
 *
 * The maximum number of elements is defined as: the number of
 * elements that can be stored in a page times the number of
 * page pointers that we can fit in the base structure or (using
 * integer math):
 *
 * 	(PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *)
 *
 * Here's a table showing example capacities.  Note that the maximum
 * index that the get/put() functions is just nr_objects-1.   This
 * basically means that you get 4MB of storage on 32-bit and 2MB on
 * 64-bit.
 *
 *
 * Element size | Objects | Objects |
 * PAGE_SIZE=4k |  32-bit |  64-bit |
 * ---------------------------------|
 *      1 bytes | 4177920 | 2088960 |
 *      2 bytes | 2088960 | 1044480 |
 *      3 bytes | 1392300 |  696150 |
 *      4 bytes | 1044480 |  522240 |
 *     32 bytes |  130560 |   65408 |
 *     33 bytes |  126480 |   63240 |
 *   2048 bytes |    2040 |    1020 |
 *   2049 bytes |    1020 |     510 |
 *       void * | 1044480 |  261120 |
 *
 * Since 64-bit pointers are twice the size, we lose half the
 * capacity in the base structure.  Also note that no effort is made
 * to efficiently pack objects across page boundaries.
 */
struct flex_array *flex_array_alloc(int element_size, unsigned int total,
					gfp_t flags)
{
	struct flex_array *ret;
	int elems_per_part = 0;
	int max_size = 0;
	struct reciprocal_value reciprocal_elems = { 0 };

	if (element_size) {
		elems_per_part = FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
		reciprocal_elems = reciprocal_value(elems_per_part);
		max_size = FLEX_ARRAY_NR_BASE_PTRS * elems_per_part;
	}

	/* max_size will end up 0 if element_size > PAGE_SIZE */
	if (total > max_size)
		return NULL;
	ret = kzalloc(sizeof(struct flex_array), flags);
	if (!ret)
		return NULL;
	ret->element_size = element_size;
	ret->total_nr_elements = total;
	ret->elems_per_part = elems_per_part;
	ret->reciprocal_elems = reciprocal_elems;
	if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
		memset(&ret->parts[0], FLEX_ARRAY_FREE,
						FLEX_ARRAY_BASE_BYTES_LEFT);
	return ret;
}
EXPORT_SYMBOL(flex_array_alloc);

static int fa_element_to_part_nr(struct flex_array *fa,
					unsigned int element_nr)
{
	/*
	 * if element_size == 0 we don't get here, so we never touch
	 * the zeroed fa->reciprocal_elems, which would yield invalid
	 * results
	 */
	return reciprocal_divide(element_nr, fa->reciprocal_elems);
}

/**
 * flex_array_free_parts - just free the second-level pages
 * @fa:		the flex array from which to free parts
 *
 * This is to be used in cases where the base 'struct flex_array'
 * has been statically allocated and should not be free.
 */
void flex_array_free_parts(struct flex_array *fa)
{
	int part_nr;

	if (elements_fit_in_base(fa))
		return;
	for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++)
		kfree(fa->parts[part_nr]);
}
EXPORT_SYMBOL(flex_array_free_parts);

void flex_array_free(struct flex_array *fa)
{
	flex_array_free_parts(fa);
	kfree(fa);
}
EXPORT_SYMBOL(flex_array_free);

static unsigned int index_inside_part(struct flex_array *fa,
					unsigned int element_nr,
					unsigned int part_nr)
{
	unsigned int part_offset;

	part_offset = element_nr - part_nr * fa->elems_per_part;
	return part_offset * fa->element_size;
}

static struct flex_array_part *
__fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
{
	struct flex_array_part *part = fa->parts[part_nr];
	if (!part) {
		part = kmalloc(sizeof(struct flex_array_part), flags);
		if (!part)
			return NULL;
		if (!(flags & __GFP_ZERO))
			memset(part, FLEX_ARRAY_FREE,
				sizeof(struct flex_array_part));
		fa->parts[part_nr] = part;
	}
	return part;
}

/**
 * flex_array_put - copy data into the array at @element_nr
 * @fa:		the flex array to copy data into
 * @element_nr:	index of the position in which to insert
 * 		the new element.
 * @src:	address of data to copy into the array
 * @flags:	page allocation flags to use for array expansion
 *
 *
 * Note that this *copies* the contents of @src into
 * the array.  If you are trying to store an array of
 * pointers, make sure to pass in &ptr instead of ptr.
 * You may instead wish to use the flex_array_put_ptr()
 * helper function.
 *
 * Locking must be provided by the caller.
 */
int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
			gfp_t flags)
{
	int part_nr = 0;
	struct flex_array_part *part;
	void *dst;

	if (element_nr >= fa->total_nr_elements)
		return -ENOSPC;
	if (!fa->element_size)
		return 0;
	if (elements_fit_in_base(fa))
		part = (struct flex_array_part *)&fa->parts[0];
	else {
		part_nr = fa_element_to_part_nr(fa, element_nr);
		part = __fa_get_part(fa, part_nr, flags);
		if (!part)
			return -ENOMEM;
	}
	dst = &part->elements[index_inside_part(fa, element_nr, part_nr)];
	memcpy(dst, src, fa->element_size);
	return 0;
}
EXPORT_SYMBOL(flex_array_put);

/**
 * flex_array_clear - clear element in array at @element_nr
 * @fa:		the flex array of the element.
 * @element_nr:	index of the position to clear.
 *
 * Locking must be provided by the caller.
 */
int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
{
	int part_nr = 0;
	struct flex_array_part *part;
	void *dst;

	if (element_nr >= fa->total_nr_elements)
		return -ENOSPC;
	if (!fa->element_size)
		return 0;
	if (elements_fit_in_base(fa))
		part = (struct flex_array_part *)&fa->parts[0];
	else {
		part_nr = fa_element_to_part_nr(fa, element_nr);
		part = fa->parts[part_nr];
		if (!part)
			return -EINVAL;
	}
	dst = &part->elements[index_inside_part(fa, element_nr, part_nr)];
	memset(dst, FLEX_ARRAY_FREE, fa->element_size);
	return 0;
}
EXPORT_SYMBOL(flex_array_clear);

/**
 * flex_array_prealloc - guarantee that array space exists
 * @fa:			the flex array for which to preallocate parts
 * @start:		index of first array element for which space is allocated
 * @nr_elements:	number of elements for which space is allocated
 * @flags:		page allocation flags
 *
 * This will guarantee that no future calls to flex_array_put()
 * will allocate memory.  It can be used if you are expecting to
 * be holding a lock or in some atomic context while writing
 * data into the array.
 *
 * Locking must be provided by the caller.
 */
int flex_array_prealloc(struct flex_array *fa, unsigned int start,
			unsigned int nr_elements, gfp_t flags)
{
	int start_part;
	int end_part;
	int part_nr;
	unsigned int end;
	struct flex_array_part *part;

	if (!start && !nr_elements)
		return 0;
	if (start >= fa->total_nr_elements)
		return -ENOSPC;
	if (!nr_elements)
		return 0;

	end = start + nr_elements - 1;

	if (end >= fa->total_nr_elements)
		return -ENOSPC;
	if (!fa->element_size)
		return 0;
	if (elements_fit_in_base(fa))
		return 0;
	start_part = fa_element_to_part_nr(fa, start);
	end_part = fa_element_to_part_nr(fa, end);
	for (part_nr = start_part; part_nr <= end_part; part_nr++) {
		part = __fa_get_part(fa, part_nr, flags);
		if (!part)
			return -ENOMEM;
	}
	return 0;
}
EXPORT_SYMBOL(flex_array_prealloc);

/**
 * flex_array_get - pull data back out of the array
 * @fa:		the flex array from which to extract data
 * @element_nr:	index of the element to fetch from the array
 *
 * Returns a pointer to the data at index @element_nr.  Note
 * that this is a copy of the data that was passed in.  If you
 * are using this to store pointers, you'll get back &ptr.  You
 * may instead wish to use the flex_array_get_ptr helper.
 *
 * Locking must be provided by the caller.
 */
void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
{
	int part_nr = 0;
	struct flex_array_part *part;

	if (!fa->element_size)
		return NULL;
	if (element_nr >= fa->total_nr_elements)
		return NULL;
	if (elements_fit_in_base(fa))
		part = (struct flex_array_part *)&fa->parts[0];
	else {
		part_nr = fa_element_to_part_nr(fa, element_nr);
		part = fa->parts[part_nr];
		if (!part)
			return NULL;
	}
	return &part->elements[index_inside_part(fa, element_nr, part_nr)];
}
EXPORT_SYMBOL(flex_array_get);

/**
 * flex_array_get_ptr - pull a ptr back out of the array
 * @fa:		the flex array from which to extract data
 * @element_nr:	index of the element to fetch from the array
 *
 * Returns the pointer placed in the flex array at element_nr using
 * flex_array_put_ptr().  This function should not be called if the
 * element in question was not set using the _put_ptr() helper.
 */
void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr)
{
	void **tmp;

	tmp = flex_array_get(fa, element_nr);
	if (!tmp)
		return NULL;

	return *tmp;
}
EXPORT_SYMBOL(flex_array_get_ptr);

static int part_is_free(struct flex_array_part *part)
{
	int i;

	for (i = 0; i < sizeof(struct flex_array_part); i++)
		if (part->elements[i] != FLEX_ARRAY_FREE)
			return 0;
	return 1;
}

/**
 * flex_array_shrink - free unused second-level pages
 * @fa:		the flex array to shrink
 *
 * Frees all second-level pages that consist solely of unused
 * elements.  Returns the number of pages freed.
 *
 * Locking must be provided by the caller.
 */
int flex_array_shrink(struct flex_array *fa)
{
	struct flex_array_part *part;
	int part_nr;
	int ret = 0;

	if (!fa->total_nr_elements || !fa->element_size)
		return 0;
	if (elements_fit_in_base(fa))
		return ret;
	for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
		part = fa->parts[part_nr];
		if (!part)
			continue;
		if (part_is_free(part)) {
			fa->parts[part_nr] = NULL;
			kfree(part);
			ret++;
		}
	}
	return ret;
}
EXPORT_SYMBOL(flex_array_shrink);
Commit	Line	Data
534acc05 DH	1	/*
	2	* Flexible array managed in PAGE_SIZE parts
	3	*
	4	* This program is free software; you can redistribute it and/or modify
	5	* it under the terms of the GNU General Public License as published by
	6	* the Free Software Foundation; either version 2 of the License, or
	7	* (at your option) any later version.
	8	*
	9	* This program is distributed in the hope that it will be useful,
	10	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	11	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	12	* GNU General Public License for more details.
	13	*
	14	* You should have received a copy of the GNU General Public License
	15	* along with this program; if not, write to the Free Software
	16	* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
	17	*
	18	* Copyright IBM Corporation, 2009
	19	*
	20	* Author: Dave Hansen <dave@linux.vnet.ibm.com>
	21	*/
	22
	23	#include <linux/flex_array.h>
	24	#include <linux/slab.h>
	25	#include <linux/stddef.h>
8bc3bcc9	26	#include <linux/export.h>
704f15dd	27	#include <linux/reciprocal_div.h>
534acc05 DH	28
	29	struct flex_array_part {
	30	char elements[FLEX_ARRAY_PART_SIZE];
	31	};
	32
534acc05 DH	33	/*
	34	* If a user requests an allocation which is small
	35	* enough, we may simply use the space in the
	36	* flex_array->parts[] array to store the user
	37	* data.
	38	*/
	39	static inline int elements_fit_in_base(struct flex_array *fa)
	40	{
	41	int data_size = fa->element_size * fa->total_nr_elements;
45b588d6	42	if (data_size <= FLEX_ARRAY_BASE_BYTES_LEFT)
534acc05 DH	43	return 1;
	44	return 0;
	45	}
	46
	47	/**
	48	* flex_array_alloc - allocate a new flexible array
	49	* @element_size: the size of individual elements in the array
	50	* @total: total number of elements that this should hold
fc0d8d94	51	* @flags: page allocation flags to use for base array
534acc05 DH	52	*
	53	* Note: all locking must be provided by the caller.
	54	*
	55	* @total is used to size internal structures. If the user ever
	56	* accesses any array indexes >=@total, it will produce errors.
	57	*
	58	* The maximum number of elements is defined as: the number of
	59	* elements that can be stored in a page times the number of
	60	* page pointers that we can fit in the base structure or (using
	61	* integer math):
	62	*
	63	* (PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *)
	64	*
	65	* Here's a table showing example capacities. Note that the maximum
	66	* index that the get/put() functions is just nr_objects-1. This
	67	* basically means that you get 4MB of storage on 32-bit and 2MB on
	68	* 64-bit.
	69	*
	70	*
	71	* Element size \| Objects \| Objects \|
	72	* PAGE_SIZE=4k \| 32-bit \| 64-bit \|
	73	* ---------------------------------\|
704f15dd JG	74	* 1 bytes \| 4177920 \| 2088960 \|
	75	* 2 bytes \| 2088960 \| 1044480 \|
	76	* 3 bytes \| 1392300 \| 696150 \|
	77	* 4 bytes \| 1044480 \| 522240 \|
	78	* 32 bytes \| 130560 \| 65408 \|
	79	* 33 bytes \| 126480 \| 63240 \|
	80	* 2048 bytes \| 2040 \| 1020 \|
	81	* 2049 bytes \| 1020 \| 510 \|
	82	* void * \| 1044480 \| 261120 \|
534acc05 DH	83	*
	84	* Since 64-bit pointers are twice the size, we lose half the
	85	* capacity in the base structure. Also note that no effort is made
	86	* to efficiently pack objects across page boundaries.
	87	*/
b62e408c DR	88	struct flex_array *flex_array_alloc(int element_size, unsigned int total,
b62e408c DR	89	gfp_t flags)
534acc05 DH	90	{
534acc05 DH	91	struct flex_array *ret;
704f15dd	92	int elems_per_part = 0;
a8d05c81	93	int max_size = 0;
809fa972	94	struct reciprocal_value reciprocal_elems = { 0 };
a8d05c81	95
704f15dd JG	96	if (element_size) {
	97	elems_per_part = FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
	98	reciprocal_elems = reciprocal_value(elems_per_part);
	99	max_size = FLEX_ARRAY_NR_BASE_PTRS * elems_per_part;
	100	}
534acc05 DH	101
	102	/* max_size will end up 0 if element_size > PAGE_SIZE */
	103	if (total > max_size)
	104	return NULL;
	105	ret = kzalloc(sizeof(struct flex_array), flags);
	106	if (!ret)
	107	return NULL;
	108	ret->element_size = element_size;
	109	ret->total_nr_elements = total;
704f15dd JG	110	ret->elems_per_part = elems_per_part;
704f15dd JG	111	ret->reciprocal_elems = reciprocal_elems;
19da3dd1	112	if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
e59464c7	113	memset(&ret->parts[0], FLEX_ARRAY_FREE,
45b588d6	114	FLEX_ARRAY_BASE_BYTES_LEFT);
534acc05 DH	115	return ret;
534acc05 DH	116	}
78c377d1	117	EXPORT_SYMBOL(flex_array_alloc);
534acc05	118
b62e408c DR	119	static int fa_element_to_part_nr(struct flex_array *fa,
b62e408c DR	120	unsigned int element_nr)
534acc05	121	{
809fa972 HFS	122	/*
	123	* if element_size == 0 we don't get here, so we never touch
	124	* the zeroed fa->reciprocal_elems, which would yield invalid
	125	* results
	126	*/
704f15dd	127	return reciprocal_divide(element_nr, fa->reciprocal_elems);
534acc05 DH	128	}
	129
	130	/**
	131	* flex_array_free_parts - just free the second-level pages
fc0d8d94	132	* @fa: the flex array from which to free parts
534acc05 DH	133	*
	134	* This is to be used in cases where the base 'struct flex_array'
	135	* has been statically allocated and should not be free.
	136	*/
	137	void flex_array_free_parts(struct flex_array *fa)
	138	{
	139	int part_nr;
534acc05 DH	140
	141	if (elements_fit_in_base(fa))
	142	return;
45b588d6	143	for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++)
534acc05 DH	144	kfree(fa->parts[part_nr]);
534acc05 DH	145	}
78c377d1	146	EXPORT_SYMBOL(flex_array_free_parts);
534acc05 DH	147
	148	void flex_array_free(struct flex_array *fa)
	149	{
	150	flex_array_free_parts(fa);
	151	kfree(fa);
	152	}
78c377d1	153	EXPORT_SYMBOL(flex_array_free);
534acc05	154
b62e408c	155	static unsigned int index_inside_part(struct flex_array *fa,
704f15dd JG	156	unsigned int element_nr,
704f15dd JG	157	unsigned int part_nr)
534acc05	158	{
b62e408c	159	unsigned int part_offset;
534acc05	160
704f15dd	161	part_offset = element_nr - part_nr * fa->elems_per_part;
534acc05 DH	162	return part_offset * fa->element_size;
	163	}
	164
	165	static struct flex_array_part *
	166	__fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
	167	{
	168	struct flex_array_part *part = fa->parts[part_nr];
	169	if (!part) {
19da3dd1	170	part = kmalloc(sizeof(struct flex_array_part), flags);
534acc05 DH	171	if (!part)
534acc05 DH	172	return NULL;
19da3dd1 DR	173	if (!(flags & __GFP_ZERO))
	174	memset(part, FLEX_ARRAY_FREE,
	175	sizeof(struct flex_array_part));
534acc05 DH	176	fa->parts[part_nr] = part;
	177	}
	178	return part;
	179	}
	180
	181	/**
	182	* flex_array_put - copy data into the array at @element_nr
fc0d8d94	183	* @fa: the flex array to copy data into
534acc05 DH	184	* @element_nr: index of the position in which to insert
534acc05 DH	185	* the new element.
fc0d8d94 DR	186	* @src: address of data to copy into the array
	187	* @flags: page allocation flags to use for array expansion
	188	*
534acc05 DH	189	*
	190	* Note that this copies the contents of @src into
	191	* the array. If you are trying to store an array of
	192	* pointers, make sure to pass in &ptr instead of ptr.
ea98eed9 EP	193	* You may instead wish to use the flex_array_put_ptr()
ea98eed9 EP	194	* helper function.
534acc05 DH	195	*
	196	* Locking must be provided by the caller.
	197	*/
b62e408c DR	198	int flex_array_put(struct flex_array fa, unsigned int element_nr, void src,
b62e408c DR	199	gfp_t flags)
534acc05	200	{
704f15dd	201	int part_nr = 0;
534acc05 DH	202	struct flex_array_part *part;
	203	void *dst;
	204
	205	if (element_nr >= fa->total_nr_elements)
	206	return -ENOSPC;
a8d05c81 EP	207	if (!fa->element_size)
a8d05c81 EP	208	return 0;
534acc05 DH	209	if (elements_fit_in_base(fa))
534acc05 DH	210	part = (struct flex_array_part *)&fa->parts[0];
a30b595d	211	else {
a8d05c81	212	part_nr = fa_element_to_part_nr(fa, element_nr);
534acc05	213	part = __fa_get_part(fa, part_nr, flags);
a30b595d DR	214	if (!part)
	215	return -ENOMEM;
	216	}
704f15dd	217	dst = &part->elements[index_inside_part(fa, element_nr, part_nr)];
534acc05 DH	218	memcpy(dst, src, fa->element_size);
	219	return 0;
	220	}
78c377d1	221	EXPORT_SYMBOL(flex_array_put);
534acc05	222
e6de3988 DR	223	/**
e6de3988 DR	224	* flex_array_clear - clear element in array at @element_nr
fc0d8d94	225	* @fa: the flex array of the element.
e6de3988 DR	226	* @element_nr: index of the position to clear.
	227	*
	228	* Locking must be provided by the caller.
	229	*/
	230	int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
	231	{
704f15dd	232	int part_nr = 0;
e6de3988 DR	233	struct flex_array_part *part;
	234	void *dst;
	235
	236	if (element_nr >= fa->total_nr_elements)
	237	return -ENOSPC;
a8d05c81 EP	238	if (!fa->element_size)
a8d05c81 EP	239	return 0;
e6de3988 DR	240	if (elements_fit_in_base(fa))
	241	part = (struct flex_array_part *)&fa->parts[0];
	242	else {
a8d05c81	243	part_nr = fa_element_to_part_nr(fa, element_nr);
e6de3988 DR	244	part = fa->parts[part_nr];
	245	if (!part)
	246	return -EINVAL;
	247	}
704f15dd	248	dst = &part->elements[index_inside_part(fa, element_nr, part_nr)];
19da3dd1	249	memset(dst, FLEX_ARRAY_FREE, fa->element_size);
e6de3988 DR	250	return 0;
e6de3988 DR	251	}
78c377d1	252	EXPORT_SYMBOL(flex_array_clear);
e6de3988	253
534acc05 DH	254	/**
534acc05 DH	255	* flex_array_prealloc - guarantee that array space exists
5a3ea878 EP	256	* @fa: the flex array for which to preallocate parts
	257	* @start: index of first array element for which space is allocated
	258	* @nr_elements: number of elements for which space is allocated
	259	* @flags: page allocation flags
534acc05 DH	260	*
	261	* This will guarantee that no future calls to flex_array_put()
	262	* will allocate memory. It can be used if you are expecting to
	263	* be holding a lock or in some atomic context while writing
	264	* data into the array.
	265	*
	266	* Locking must be provided by the caller.
	267	*/
b62e408c	268	int flex_array_prealloc(struct flex_array *fa, unsigned int start,
5a3ea878	269	unsigned int nr_elements, gfp_t flags)
534acc05 DH	270	{
	271	int start_part;
	272	int end_part;
	273	int part_nr;
5a3ea878	274	unsigned int end;
534acc05 DH	275	struct flex_array_part *part;
534acc05 DH	276
150cdf6e EP	277	if (!start && !nr_elements)
	278	return 0;
	279	if (start >= fa->total_nr_elements)
	280	return -ENOSPC;
	281	if (!nr_elements)
	282	return 0;
	283
5a3ea878 EP	284	end = start + nr_elements - 1;
5a3ea878 EP	285
150cdf6e	286	if (end >= fa->total_nr_elements)
534acc05	287	return -ENOSPC;
a8d05c81 EP	288	if (!fa->element_size)
a8d05c81 EP	289	return 0;
534acc05 DH	290	if (elements_fit_in_base(fa))
	291	return 0;
	292	start_part = fa_element_to_part_nr(fa, start);
	293	end_part = fa_element_to_part_nr(fa, end);
	294	for (part_nr = start_part; part_nr <= end_part; part_nr++) {
	295	part = __fa_get_part(fa, part_nr, flags);
	296	if (!part)
	297	return -ENOMEM;
	298	}
	299	return 0;
	300	}
78c377d1	301	EXPORT_SYMBOL(flex_array_prealloc);
534acc05 DH	302
	303	/**
	304	* flex_array_get - pull data back out of the array
fc0d8d94	305	* @fa: the flex array from which to extract data
534acc05 DH	306	* @element_nr: index of the element to fetch from the array
	307	*
	308	* Returns a pointer to the data at index @element_nr. Note
	309	* that this is a copy of the data that was passed in. If you
ea98eed9 EP	310	* are using this to store pointers, you'll get back &ptr. You
ea98eed9 EP	311	* may instead wish to use the flex_array_get_ptr helper.
534acc05 DH	312	*
	313	* Locking must be provided by the caller.
	314	*/
b62e408c	315	void flex_array_get(struct flex_array fa, unsigned int element_nr)
534acc05	316	{
704f15dd	317	int part_nr = 0;
534acc05	318	struct flex_array_part *part;
534acc05	319
a8d05c81 EP	320	if (!fa->element_size)
a8d05c81 EP	321	return NULL;
534acc05 DH	322	if (element_nr >= fa->total_nr_elements)
534acc05 DH	323	return NULL;
534acc05 DH	324	if (elements_fit_in_base(fa))
534acc05 DH	325	part = (struct flex_array_part *)&fa->parts[0];
a30b595d	326	else {
a8d05c81	327	part_nr = fa_element_to_part_nr(fa, element_nr);
534acc05	328	part = fa->parts[part_nr];
a30b595d DR	329	if (!part)
	330	return NULL;
	331	}
704f15dd	332	return &part->elements[index_inside_part(fa, element_nr, part_nr)];
534acc05	333	}
78c377d1	334	EXPORT_SYMBOL(flex_array_get);
4af5a2f7	335
ea98eed9 EP	336	/**
	337	* flex_array_get_ptr - pull a ptr back out of the array
	338	* @fa: the flex array from which to extract data
	339	* @element_nr: index of the element to fetch from the array
	340	*
	341	* Returns the pointer placed in the flex array at element_nr using
	342	* flex_array_put_ptr(). This function should not be called if the
	343	* element in question was not set using the _put_ptr() helper.
	344	*/
	345	void flex_array_get_ptr(struct flex_array fa, unsigned int element_nr)
	346	{
	347	void **tmp;
	348
	349	tmp = flex_array_get(fa, element_nr);
	350	if (!tmp)
	351	return NULL;
	352
	353	return *tmp;
	354	}
78c377d1	355	EXPORT_SYMBOL(flex_array_get_ptr);
ea98eed9	356
4af5a2f7 DR	357	static int part_is_free(struct flex_array_part *part)
	358	{
	359	int i;
	360
	361	for (i = 0; i < sizeof(struct flex_array_part); i++)
	362	if (part->elements[i] != FLEX_ARRAY_FREE)
	363	return 0;
	364	return 1;
	365	}
	366
	367	/**
	368	* flex_array_shrink - free unused second-level pages
fc0d8d94	369	* @fa: the flex array to shrink
4af5a2f7 DR	370	*
	371	* Frees all second-level pages that consist solely of unused
	372	* elements. Returns the number of pages freed.
	373	*
	374	* Locking must be provided by the caller.
	375	*/
	376	int flex_array_shrink(struct flex_array *fa)
	377	{
	378	struct flex_array_part *part;
4af5a2f7 DR	379	int part_nr;
	380	int ret = 0;
	381
a8d05c81	382	if (!fa->total_nr_elements \|\| !fa->element_size)
150cdf6e	383	return 0;
4af5a2f7 DR	384	if (elements_fit_in_base(fa))
4af5a2f7 DR	385	return ret;
45b588d6	386	for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
4af5a2f7 DR	387	part = fa->parts[part_nr];
	388	if (!part)
	389	continue;
	390	if (part_is_free(part)) {
	391	fa->parts[part_nr] = NULL;
	392	kfree(part);
	393	ret++;
	394	}
	395	}
	396	return ret;
	397	}
78c377d1	398	EXPORT_SYMBOL(flex_array_shrink);